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Ruby Programming
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Variable Scope and Loops

The while, until, and for loops are built into the language and do not introduce new scope; previously existing locals can be used in the loop, and any new locals created will be available afterward.

The blocks used by iterators (such as loop and each) are a little different. Normally, the local variables created in these blocks are not accessible outside the block.

[ 1, 2, 3 ].each do |x|
  y = x + 1
[ x, y ]
prog.rb:4: undefined local variable or method `x'
for #<Object:0x401c2ce0> (NameError)

However, if at the time the block executes a local variable already exists with the same name as that of a variable in the block, the existing local variable will be used in the block. Its value will therefore be available after the block finishes. As the following example shows, this applies both to normal variables in the block and to the block's parameters.

x = nil
y = nil
[ 1, 2, 3 ].each do |x|
  y = x + 1
[ x, y ] [3, 4]

Ruby Programming
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